AlNiCo magnets have been mass-produced for over 50 years. Their name comes from the alloy composition of which they are manufactured. They contain: 7-10% Al, 13-16% Ni, 20-40% Co, being Fe the remaining constituent. Besides, Alnico magnet contains such additions like Cu (3-5%), Ti (1-8%) and Nb, or Ta. For their production employed can be either metallurgical methods (casting), or powder metallurgy (sintering). At present, most often, they are manufactured as anisotropic magnets.
From among all types of magnets, alnico magnets are characteristic of the highest temperature stability of magnetic parameters, very high Curie Tc temperature, as well as maximum working temperature Tmax, related to to the last one. They are also marked out by the highest corrosion resistance. Maximum values of their energy density (BH)max are a bit higher or similar to those of (BH)max for ferrite magnets, while values of their remanence Br are similar to those of Sm-Co sintered magnets. Their reverse permeability is 2,7 times bigger than that of other magnets. However, small values of coercive force jHc make impossible to apply alnico magnets in the presence of strong demagnetizing fields, which limits their applications. Moreover, their low coercive force affects determination of the working point of alnico magnets. Low (flat) alnico magnets, immediately after taken out of the field magnet get considerably demagnetized, and their working point is determined far less than the value of remanence of magnetic flux density. They suffer demagnetization also when have been wrapped or hit, and that is why, in practice, applied are mostly high alnico magnets, that are more resistant to such effects, or they are installed in magnetic circuits and then magnetized, which makes possible determination of their working point close to the remanence Br value.
Alnico magnets predominate over other types of magnets thanks to their temperature stability of magnetic parameters, maximum working temperature Tmax and corrosion resistance.
First of all, they are installed in measuring instruments, control devices, various converters and sensors, motors and generators, and many other appliances (systems), that require stable magnetic field in relation to temperature, and when there is enough space to find room for magnets.Magnetic and physical properties typical for cast alnico magnets:
Magnetic and physical properties typical for sintered alnico magnets: